Method of treating crystalline abrasives and treated product



Patented Jan. 28, 1936 IVIETHOD OF TREATING CBYSTALLINE ABBASIVES AND TREATED PRODUCT Charles R. Walker, South Braintree, Mass., asslgnor to Abrasive Products, Inc., South Braintree, Mass., a corporation of Massachusetts No Drawing. Application August 30, 1935, Serial No. 38,658

crystalline abrasives such as garnet, silicon carbide, aluminous oxide, and the like prior to the usual step of crushing or grinding the same to grain sizes, and contemplates a method of treatment whereby the uncrushed crystalline mineral is caused to fracture along natural cleavage planes, and thus be capable of more ready groundng or crushing to grain sizes suitable for bond- Kg into abrasive papers, grinding wheels or the As a result of my treatment the capillarity of the crystalline abrasive mineral is materially improved. Moreover when the mineral is crushed or ground to grain sizes, the naturally sharp cutting edges are preserved and exist in the ground material as hard, tough, sharp cutting edges of increased cutting efiiciency as compared with crystalline material which has been crushed or ground to grain sizes without preliminary treatment in accordance with my invention to cause it to fracture along natural cleavage planes.

With some crystalline minerals, my treatment has the effect of materially increasing the hard:

ness and life of the abrasive.

Lindsey in 1887 (Patent No. 273,239) disclosed a process of grinding and polishing-steel involving the use of heat treatment to cause the steel to crystallize and thus break easily.

My invention deals, however, with the treatment of already crystallized minerals to cause them to fracture along. natural cleavage planes. By it I avoid the necessity of using crushing rollers, ball mills, pan mills, tube mills, and the like. in the first or rough crushing step. Instead I subject the uncrushed crystalline abrasive material to an oxidizing temperature and there plished by agitation of the material, for a sufficient length of time to thoroughly heat it.

The oxidizing temperature may be from 1300 to 1500" F., more or less, and the time of treat ment ma extend from five to ten minutes morey crushed crystalline abrasive, which consists in 50 or less.

The heated material is then suddenly quenched in cold water. Ordinarily the water has a temperature of from 50 to 60 F., more or less, although the colder the water the more sharp or sudden the reaction. The material is left in thiswater until it is sufliciently chilled so that it may be comfortably handled. This may be and frequently is a matter of one hour, more or less.

As a result of these sudden temperature changes, the material splits along its natural 5 cleavage planes. In this action apparently the water seeps into the cleavage lines and the steam generated by the contact of the heated material with the cold water explosively disrupts the crys talline material along such cleavage lines, after 10 which the split pieces are dried in any suitable manner and crushed or ground to size.

Uncrushed crystalline abrasive minerals treated in accordance with my method are of increased capillarity and far greater abrasive ca- 15 pacity than untreated materials or materials treated by the usual methods.

The hardness and sharpness ofthe natural cutting edges is preserved and the cutting efficiency is consequently greatly increased, as is '20 its useful life when crushed to grain sizes and fabricated into abrasive papers or the like. More than this its aflinity for the cement, adhesive or other bonding agent commonly used to bond the grains to the paper or fabric backing is greater. 25

While I have disclosed the best method of practicing my invention now known to me, it will be understood that the times and temperatures stated are illustrative and not critical and may be various according to the nature of the 30 crystalline mineral being treated and the particular characteristics wanted in the final product. Such disclosure therefore is to be regarded as suggestive only. Thus various modifications in procedure may be resorted to if within the 35 spirit and scope of my invention as defined by the appended claims.

What I therefore claim and desire to secure by Letters Patent is:

1. That step in the method of producing uncrushed crystalline abrasive, which consists in subjecting the same to sudden extremes of tem perature change to produce a re-action effective to cause the material to fracture along natural cleavage planes and to be capable of ready crushing without destruction of the naturally sharp cutting edges at such planes of fracture.

2. The steps in the method of producing unfirst heating the same at an oxidizing temperature and thereafter suddenly quenching the same to produce a reaction effective to cause the material to fracture along natural cleavage planes and to be capable of ready crushing without 55 destruction of the naturally sharp cutting edges at such planes of fracture. r

3. The method of producing uncrushed crystalline abrasive, which consists in first heating the, same at an oxidizing temperature and thereafter suddenly quenching the same to produce a reaction efi'ective to cause the material to fracture along natural cleavage planes and to be capable of ready crushing without destruction of the naturally sharp cutting edges at such planes of fracture, in drying the fractured pieces and in crushing the same to grain size.

4. The method of claim 3 wherein the heat treatment temperature is from 1300 to 150 F., more or less.

5. The method of claim 3 wherein the heat treatment temperature is from 1300 to 150 ll F., more or less and wherein the temperature 01 the quenching fluid is from 50 to 60 F., more or less. I

6. The method of claim 3 wherein the time of heat treatment is from 5 to minutes, more or less. a

7. The method of claim 3 wherein the time of heat treatment is from 5 to 10 minutes more or less and the temperature is from 1300 to 1500 F.

-8. As a new abrasive uncrushed crystalline abrasive material having its lines of fracture along natural cleavage planes so that it may be readily crushed without destruction of the naturally sharp cutting edges at such planes of fracture.

9. As a new abrasive, crushed crystalline abrasive material having its lines of fracture along natural cleavage planes and crushed without destruction of the naturally sharp cutting edges at such planes of fracture. V

CHARLES R 

